Silicon wafer horizontal growth apparatus and method

ABSTRACT

A silicon wafer horizontal growth apparatus comprises a casing forming a cavity; a crucible within the cavity and having a melting zone, an overflow port, a first and a second overflow surface; a feeding assembly for adding raw material to the melting zone at an adjustable rate; a heating assembly comprising two movable heaters disposed on the upper and lower sides of the crucible at an interval; a thermal insulation component for maintaining a temperature in the cavity; a gas flow assembly comprising a jet located above the second overflow surface, a gas conductive graphite member mounted on the bottom of the crucible, a quartz exhaust tube connected with the gas conductive graphite member, and a quartz cooling tube outside the exhaust tube; and a heat insulating baffle located above the second overflow surface for isolating the heating assembly from the jet, dividing the cavity into hot and cold zones.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation application of International Application SerialNo. PCT/CN2017/095869, filed on Aug. 3, 2017, which claims the benefitof Chinese Application No. 201710300122.6, filed on Apr. 28, 2017, thedisclosures of which are hereby incorporated by reference.

BACKGROUND Field of the Invention

The present application relates to the field of silicon materialfabricating technology, and in particular, to a silicon wafer horizontalgrowth apparatus and method.

Description of the Related Art

Silicon as a non-metal material has a wide range of applications in thesemiconductor field as well as in the photovoltaic field. In the priorart, a monocrystalline silicon ingot is typically produced by aCzochralski method (CZ method) or a zone melting method (HZ method), anda polycrystalline silicon ingot is typically produced by a castingtechnique.

In the prior art, a silicon wafer having a certain thickness is obtainedby a technique such as wire cutting, grinding and polishing, and thelike, and a large amount of raw materials are wasted in the process ofpost-processing, thereby causing a substantial increase in theproduction cost of the silicon wafer. In order to reduce the loss ofmaterials, various methods for direct fabrication of silicon wafers suchas Edge-defined Film-fed Growth (EFG) and String Ribbon Growth (SR),have been developed, but mass production has not yet been achieved. In1950, another method for the direct growth of silicon wafers, HorizontalRibbon Growth (HRG), was proposed. Based on this method, an experimentalfabrication apparatus was designed in 1960, but the horizontal growth ofthe silicon ribbon could not be achieved. In 2016, Clarkson Universityproposed a method for growing silicon wafers by horizontal floatingsilicon technique, and carried out numerical simulations andexperiments, which are described in non-patent Document 1. However, theshape of the silicon wafer grown by the horizontal floating silicontechnique has obvious defects and a large thickness, which requiressubsequent cutting processing.

Non-Patent Literature 1

Helenbrook B T, Kellerman P, Carlson F, et al. Experimental andnumerical investigation of the horizontal ribbon growth process [J].Journal of Crystal Growth, 2016, 453:163-172.

BRIEF SUMMARY

In view of the problems existing in the field of existing horizontallygrown silicon wafers, such as unstable growth, large shape defects, andexcessive thickness, the present application discloses an apparatus anda method for horizontally growing a silicon wafer continuously with athickness controllable. The upper and lower radiant heating and jetcooling methods are used to control the temperature field and the flowfield so as to control the thickness of the silicon wafer. The thicknessof the silicon wafer is ensured to be uniform and the upper and lowersurfaces of the silicon wafer are ensured to be smooth by using amulti-stage melting region and a two-stage overflow surface and bysmoothing the temperature field by an external pumping gas.

A silicon wafer horizontal growth apparatus of the present applicationcomprises: a casing forming a cavity; a crucible, located in the cavityand having a melting zone, an overflow port, a first overflow surfaceand a second overflow surface; a feeding assembly for adding silicon rawmaterial to the melting zone at a feeding rate adjustable; a heatingassembly comprising two movable heaters, the two movable heaters aredisposed on the upper and lower sides of the crucible at a certaininterval with the crucible; a thermal insulation component formaintaining a temperature in the cavity; a gas flow assembly comprisinga jet, a gas conductive graphite member, a quartz exhaust tube, and aquartz cooling tube, wherein the jet is located above the secondoverflow surface, the gas conductive graphite member is mounted on thebottom of the crucible, the quartz cooling tube is nested outside thequartz exhaust tube, the quartz exhaust tube is connected with the gasconductive graphite member; and a heat insulating baffle located abovethe second overflow surface for isolating the heating assembly and thejet so that the cavity is divided into two temperature zones of a hotzone and a cold zone.

Preferably, the apparatus further comprises a receiving crucible locatedbelow an edge of the second overflow surface of the crucible.

Preferably, a heat conductive graphite plate is disposed between theheater and the crucible.

Preferably, a distance between the heater and the crucible is in a rangeof 1 to 5 mm.

Preferably, a distance between the jet and the second overflow surfaceis greater than 7 mm.

Preferably, the heat insulating baffle has a thickness in a range of 1to 3 cm.

Preferably, a distance between the heat insulating baffle and the secondoverflow surface is in a range of 2 to 6 mm.

Preferably, the jet includes a gas inflow tube, a jet tube and a supporttube, wherein two ends of the jet tube are respectively connected to theinflow tube and the support tube through a connecting member, and thejet tube has a double-layered structure with an outer layer being madeof an isostatically pressed graphite material, and an inner layer beingmade of ceramic or high-density graphite material, and the jet tube isprovided with a row of holes or a slit.

A method for horizontal growth of a silicon wafer of the presentapplication comprises the steps of: a step of melting a silicon rawmaterial including: adding the silicon raw material to a melting zone ofa crucible through a feeding assembly; introducing a reducing gas into acavity through a quartz cooling tube to place the cavity in a reducingatmosphere; then heating by a heater; when the temperature is stabilizedat a set temperature and the silicon material is completely melted, anew silicon material is slowly added through a feeding port, so that themolten silicon material flows from an overflow port to a first overflowsurface; as the silicon material gradually increases, the molten silicongradually increases accordingly, the silicon material overflows to thesecond overflow surface smoothly; and a step of horizontal drawing ofthe silicon wafer, including: when the silicon material is about toreach a boundary between a cold zone and hot zone, a seed plate isinserted into the cavity, and a rate of feeding is slowed down, so thata melted material flows slowly to the seed plate in a thin layer; whenthe melted material contacts a seed ingot, the seed plate is pulledbackward, and at the same time, the jet and the air pump are turned on,and a quartz exhaust tube is exhausted by pumping outwardly, and thequartz cooling tube is always kept in a ventilated state.

Preferably, an average temperature of the hot zone is in a range of1500° C. to 1600° C., and an average temperature of the cold zone is ina range of 800° C. to 1000° C.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a functional block diagram of a silicon wafer horizontalgrowth apparatus according to an embodiment of the invention.

FIG. 2 is a front view of the silicon wafer horizontal growth apparatus.

FIG. 3 is a cabinet drawing of the silicon wafer horizontal growthapparatus.

FIG. 4 is a cabinet drawing of an assembly drawing of a crucible and agas guiding graphite component of the silicon wafer horizontal growthapparatus.

FIG. 5 is a cabinet drawing of a jet assembly drawing of the siliconwafer horizontal growth apparatus.

FIG. 6 is a flow chart of a method of horizontal growth of a siliconwafer.

DETAILED DESCRIPTION

In order to make clear the object, the technical solution and theadvantages of the present invention, embodiments of the presentinvention will be clearly and completely described in the following withreference to the accompanying drawings. It should be understood that theexamples herein are only intended to illustrate the invention and arenot intended to limit the invention. The described embodiments are onlya part of the embodiments of the invention, but not all of theembodiments. All other embodiments obtained by those skilled in the artbased on the embodiments of the present invention without creativeefforts are within the scope of the present invention.

It is to be understood that in the description of the present invention,the orientations or positional relationships of the terms “upper”,“lower”, “bottom”, “horizontal”, “inside”, “outside”, etc. are based onthe orientation or positional relationships in the accompanyingdrawings, and are merely for the purpose of describing the presentinvention and simplifying the description, rather than indicating orimplying that a device or a component must be in a particularorientation, be constructed or operate in a particular orientation.Thus, these terms should not be construed as liming the invention.Moreover, the terms “first” and “second” and the like are used fordescriptive purposes only and are not to be construed as indicating orimplying relative importance.

In the description of the present invention, it should be noted that theterms “assemble”, “connect”, and “couple” are to be understood broadly,unless otherwise specified or clearly defined. For example, they canrefer to fixed or detachable connection, integral connection, mechanicalor electrical connection; direct connection or indirect connectionthrough an intermediate medium, or refer to internal communication oftwo components. For those skilled in the art, the specific meaning ofthe above terms in the present invention should be understood based onspecific circumstances.

In addition, the present disclosure provides examples of variousspecific processes and materials, but the invention may be practicedwithout these specific details, as will be understood by those skilledin the art. Unless otherwise indicated below, various portions orcomponents of the apparatus can be implemented using processes andmaterials well known in the art.

FIG. 1 is a functional block diagram of a silicon wafer horizontalgrowth apparatus according to an embodiment of the present invention.The basic principle of the silicon wafer horizontal growth apparatus ofthe present invention will be described below with reference to FIG. 1.As shown in FIG. 1, a crucible 10 of the silicon wafer horizontal growthapparatus of the present invention has a melting zone 1, an overflowport 2, a first overflow surface 3, and a second overflow surface 4.These designs of multi-stage melting zones and two-stage overflowsurfaces ensure the silicon wafer to have a uniform thickness and smoothupper and lower surfaces. A cavity of the apparatus is divided by a heatinsulating baffle 17 into two temperature zones of a hot zone 8 and acold zone 9. An upper heater 11 and a lower heater 12 are respectivelydisposed above and below the crucible 10 in the hot zone 8. A jet port35 is provided above the second overflow surface 4 of the crucible 10 inthe cold zone. By the upper and lower radiant heating and jet cooling,the temperature field and the flow field can be controlled, thereby thethickness of the silicon wafer can be controlled. Furthermore, theprovision of ventilation holes 40, 41 ensures that a large amount of gasgenerated by the jet does not have too much influence on the pressureinside the cavity.

FIG. 2 is a front view of the silicon wafer horizontal growth apparatusof the present embodiment, FIG. 3 is a cabinet drawing of the siliconwafer horizontal growth apparatus, and FIG. 4 is a cabinet drawing of anassembly drawing of the crucible and the gas guiding graphite componentof the silicon wafer horizontal growth apparatus. The specific structureof the silicon wafer horizontal growth apparatus of the presentembodiment will be described in detail below with reference to FIGS.2-4. As shown in FIG. 2, FIG. 3 and FIG. 4, the silicon wafer horizontalgrowth apparatus of the present embodiment comprises an aluminum casing(not shown), a water cooling device (not shown) for cooling the casing,the crucible 10, the upper heater 11, the lower heater 12, graphiteheater guiding rails 18, 19, 20, 21, graphite electrodes 22, 23, 24, 25,a quartz exhaust tube 13, a quartz cooling tube 14, an jet 15, an gasguiding graphite element 16, an insulation baffle 17, an feedinggraphite assembly 27, and a thermal insulation assembly. Among them, thegraphite electrodes 22, 23, 24, 25 are connected to an external workingcircuit, and are connected to the wires for passing current through aspecific connecting device. The thermal insulation assembly includes abottom insulation member 32, a right inner insulation member 30, and aright outer insulation member 29. The thermal insulation component ismade of heat insulating graphite felt to isolate part of heat of thethermal field from dissipating outward from the bottom of the outercasing and a crystal drawing opening.

As shown in FIG. 2, the silicon material enters from a feeding port 5 ofthe feeding graphite assembly 27, and is drawn out from an outlet 37after the silicon wafer is formed. The upper heater 11 and the lowerheater 12 are supported by graphite heater guiding rails 18, 19, 20, 21,and the two heaters can be moved on the guiding rails. This designallows the upper and lower heaters to form a thermal field environmentrequired for different processes. Further, as shown in FIG. 2, thequartz cooling tube 14 may be nested outside the quartz exhaust tube 13.The quartz cooling tube 14 also cools the quartz exhaust tube 13 whileintroducing a reducing gas into the cavity, thereby ensuring that thequartz tube will not deform due to high temperature during thefabrication process.

As shown in FIG. 3, the crucible 10 is supported by the heat insulatingmember and is not in direct contact with the upper heater 11 and thelower heater 12. However, in order to ensure the heating efficiency, theheaters should be positioned as close as possible to the boundaries ofthe upper heating zone and the lower heating zone, and the spacing canbe controlled in the range of 1 to 5 mm. A distance between the jet 15and the second overflow surface 4 (i.e., the working surface) istypically greater than 7 mm so as to reduce the effect of the jet flowon the smoothness of the surface. The flow rate of the jet is adjustableso that different temperature gradients can be formed between the hotzone 8 and the cold zone 9 through different flow rates, and siliconbodies of different thicknesses can be prepared at a constant drawingspeed. In addition, the jet 15 is half-wrapped by the heat insulatingbaffle 17 and the heat insulating members on both sides, and the lowerend of the heat insulating baffle 17 is about 2 to 6 mm away from thesecond overflow surface 4. This design can prevent the flow field changecaused by strong convection of the jet 15 from influencing the hot zone8 and resulting in an uneven thermal field of the hot zone 8, whileensuring that the melt smoothly passes by. The insulating baffle 17 hasa thickness in a range of 1 to 3 cm. A sufficient thickness can ensurethat an excessive temperature gradient is not formed between the hotzone 8 and the cold zone 9. Such a design can effectively improve thestability of the thermal field of the hot zone 8, thereby making iteasier to obtain a silicon wafer having a smooth appearance.

Further, the silicon wafer horizontal growth apparatus of the presentinvention may further include a thermal conductive graphite plate 26. Asshown in FIG. 3, both the upper heater 11 and the lower heater 12 aremeandering-type graphite heaters, and are made of isostatic pressuregraphite such as G430. Since the heaters are of meandering type, itcauses uneven radiation. Therefore, a high thermal conductive graphiteplate 26 is added between the upper heater 11 and the surface of thecrucible 10. The surface of the melt is heated by the heat conductivegraphite plate, which can effectively solve the problem of uneventhermal field due to uneven radiation.

Further, the silicon wafer horizontal growth apparatus of the presentinvention further includes a receiving crucible 28. As shown in FIG. 3,due to the presence of the upper heater 11 and the lower heater 12during the fabrication process, the heat supplied causes the crucible 10to be in an “overheated” state, and there will be a thin liquid filmbetween the formed silicon wafer and the second overflow surface 4.Therefore, a receiving crucible 28 is placed under an edge 31 of thecrucible to prevent the outflowing solution from contaminating theinsulating layer. At the edge 31 of the crucible, the edge is machinedwith a chamfer with an angle of 20° to 90°. This design allows a stablemeniscus to be formed at the edge when the silicone fluid flows out.

As shown in FIG. 4, the gas conductive graphite member 16 is fitted atthe bottom of the crucible 10. The crucible 10 includes a melting zone1, an overflow port 2, a first overflow surface 3, and a second overflowsurface 4. The gas conductive graphite member 16 is provided with aquartz exhaust tube connection ports 33, 34, a gas guiding grooves 38,39 and a gas intake ports 40, 41. The quartz exhaust tube connectionports 33, 34 are connected to the quartz exhaust tube 13. The siliconmaterial melted in the melting zone 1 flows out from the overflow port2, and is buffered by the first overflow surface to weaken the liquidlevel fluctuation caused by the feeding, and then flows into the secondoverflow surface 4 to contact the seed crystal. Thereafter, the drawingprocess for a chip is started. During the drawing process, the infraredthermometer detects the hot zone temperature measurement point 6 and thecold zone temperature measurement point 7 (as shown in FIG. 3)respectively and feeds back to the system. At the same time, the gasjetted from the jet 15 is sucked through the intake ports 40, 41, andflows out from the connection ports 33, 34 through the guidance of thegas guide grooves 38, 39. During the drawing, the gas is pumped outwardby the quartz exhaust tube 13 continuously so as to ensure that a largeamount of gas generated by the jet flow will not have too much influenceon the pressure in the furnace cavity. During this process, the tensionformed by the pumping will make the connection between the gasconductive graphite member 16 and the crucible 10 tighter, and at thesame time, the thermal field of the second overflow surface 4 will besmoother, and this design allows a stable growth of the silicon waferduring the drawing process so as to form a silicon wafer having a smoothsurface topography.

FIG. 5 is a cabinet drawing of an assembly drawing of a jet of a siliconwafer horizontal growth apparatus. The specific structure of the jetwill be described below with reference to FIG. 5. As shown in FIG. 5,the jet 15 includes a gas inflow tube 151, a jet tube 152, a supporttube 153, and two connectors 154. The overall material of the jet 15 isisostatically pressed graphite. The presence of the support tube 153ensures that the jet will not be damaged by vibration during the largeflow gas jet, and the life of the jet can be effectively improved. Thehigh-temperature gas required for the jet cooling is introduced from ajet gas introduction port 36 of the gas inflow tube 151. The jet tube152 of the jet 15 has a two-layered structure, the outside layer isisostatically pressed graphite, the inner layer is nested with ceramictube or high-density graphite. The nested structure can prevent thethermal stress caused by a large temperature gradient formed duringpassage of the jet gas from destroying the graphite structure. The jetport 35 may adopt a row of holes or a slit structure, and the jet 15shown in FIG. 5 employs a jet port of a slit jet type. This design ofthe jet port can ensure the heat exchange amount without causing obviousshape defects of the drawn silicon wafer.

According to another aspect of the present invention, a method ofhorizontal growth of a silicon wafer is also disclosed. The details willbe specifically described below with reference to FIG. 6. FIG. 6 is aflow chart of a method of horizontal growth of a silicon wafer. First,in a step of melting silicon raw material S1, at first, the powderysilicon material is filled in the melting zone 1 in an amount of 100 to180 g; after the assembly is completed, the reducing gas such as heliumgas or argon gas, etc., is continuously supplied from the quartz coolingtube 14, so that the furnace cavity is placed in a reducing atmosphere;after supplying gas for 5 to 10 minutes, the graphite resistance heatingsystem is turned on, and the heat field setting temperature is set to1500 to 1600° C., and the upper heater 11 and the lower the heater 12heats the overall thermal field and the silicon raw material to providesufficient heat for the thermal field to rapidly melt the added siliconmaterial; when the temperature is stable at the set temperature and thesilicon material is completely melted, new silicon material is slowlyadded from the feeding port 5 so that the melted silicon material flowsvia the overflow port 2 to the first overflow surface 3; as the siliconmaterial gradually increases, the melted silicon gradually increases,and the silicon material flows from a slope to the second overflowsurface 4. At this time, the silicon, after being buffered by the firstoverflow surface, will flow into the crystal growth zone in a relativelysmooth state.

Next, in a step of horizontally drawing silicon wafer S2, since the heatinsulating baffle 17 is placed between the jet 15 and the heatingregion, the entire thermal field is divided into the hot zone 8 and thecold zone 9, and the hot zone 8 has an average temperature of 1500 to1600° C., and the cold zone 9 has an average temperature of 800 to 1000°C. When the silicon material is about to reach the cold zone (i.e., theboundary of the hot zone), the seed plate is inserted into the furnacecavity (depending on the feeding rate, an arrival time needs to beadjusted), and at the same time the feeding rate is slowed down toensure the melt to flow slowly in a thin layer toward the seed crystal;when the melt is in contact with the seed ingot, the seed is pulled in areverse direction, and at the same time the jet 15 is turned on. Theflow rate of the jet 15 is set to, for example, 0 to 3 m3/min, and thejet gas is pure inert gas of 600-1000° C. or a mixed gas of two inertgases mixed in a certain proportion; a gas pump is turned on at the sametime as the jet 15 is turned on, and the gas is pumped outward throughthe quartz exhaust tube 13 to ensure that the internal pressure will notbe too large, and the gas will not be too much, and the quartz coolingtube 14 is always kept in a ventilated state, and the silicon wafer canbe continuously drawn horizontally.

The above is only a specific embodiment of the present invention, butthe scope of the present invention is not limited thereto. It isintended that any change or substitution easily considered by thoseskilled in the art in the light of the disclosure of the presentapplication should be within the scope of the present invention

What is claimed is:
 1. A silicon wafer horizontal growth apparatus,comprising: a casing forming a cavity; a crucible, located in the cavityand having a melting zone, an overflow port, a first overflow surfaceand a second overflow surface; a feeding assembly for adding silicon rawmaterial to the melting zone at a feeding rate adjustable; a heatingassembly comprising two movable heaters, the two movable heaters beingdisposed on the upper and lower sides of the crucible respectively at acertain interval with the crucible; a thermal insulation component formaintaining a temperature in the cavity; a gas flow assembly comprisinga jet, a gas conductive graphite member, a quartz exhaust tube, and aquartz cooling tube, wherein the jet is located above the secondoverflow surface, the gas conductive graphite member is mounted on thebottom of the crucible, the quartz cooling tube is nested outside thequartz exhaust tube, and the quartz exhaust tube is connected with thegas conductive graphite member; and a heat insulating baffle locatedabove the second overflow surface for isolating the heating assemblyfrom the jet so that the cavity is divided into two temperature zones ofa hot zone and a cold zone.
 2. The apparatus according to claim 1,further comprising a receiving crucible located below an edge of thesecond overflow surface of the crucible.
 3. The apparatus according toclaim 1, wherein a heat conductive graphite plate is disposed betweenthe heater and the crucible.
 4. The apparatus according to claim 1,wherein a distance between the heater and the crucible is in a range of1 to 5 mm.
 5. The apparatus according to claim 1, wherein a distancebetween the jet and the second overflow surface is greater than 7 mm. 6.The apparatus according to claim 1, wherein the heat insulating bafflehas a thickness in a range of 1 to 3 cm.
 7. The apparatus according toclaim 1, wherein a distance between the heat insulating baffle and thesecond overflow surface is in a range of 2 to 6 mm.
 8. The apparatusaccording to claim 1, wherein the jet includes a gas inflow tube, a jettube and a support tube, wherein two ends of the jet tube arerespectively connected to the inflow tube and the support tube through aconnecting member, and the jet tube has a double-layered structure withan outer layer being made of an isostatically pressed graphite material,and an inner layer being made of ceramic or high-density graphitematerial, and the jet tube is provided with a row of holes or a slit. 9.A method for horizontal growth of a silicon wafer, comprising: a step ofmelting a silicon raw material, including: adding a silicon raw materialto a melting zone of a crucible through a feeding assembly; introducinga reducing gas into a cavity through a quartz cooling tube to place thecavity in a reducing atmosphere; then heating by a heater; when thetemperature is stabilized at a set temperature and the silicon materialis completely melted, a new silicon material is slowly added through afeeding port, so that the molten silicon material flows from an overflowport to a first overflow surface; as the silicon material graduallyincreases, the molten silicon gradually increases accordingly, thesilicon material overflows to a second overflow surface smoothly; and astep of horizontal drawing of the silicon wafer, including: when thesilicon material is about to reach a boundary between a cold zone andhot zone, a seed plate is inserted into the cavity, and at the sametime, a rate of feeding is slowed down, so that a melted material flowsslowly to the seed plate in a form of a thin layer; when the meltedmaterial contacts the seed plate, the seed plate is pulled backward, andat the same time, a jet and an air pump are turned on, and a quartzexhaust tube is exhausted by pumping outwardly, and the quartz coolingtube is always kept in a ventilated state.
 10. The method according toclaim 9, wherein an average temperature of the hot zone is in a range of1500° C. to 1600° C., and an average temperature of the cold zone is ina range of 800° C. to 1000° C.